This invention relates to a tubular shaped shock-absorber of the liquid-operated type and having adjustable resistance to motion, which is suitable for various applications and particularly as a physical training appliance.
Numerous shock-absorbers are known and their manufacture has developed considerably with the growth of the motor vehicle industry. The problem of adjusting or regulating their resistance is not a simple one, however, and there are no known industrial shock-absorbers which can be adjusted or regulated very quickly and conveniently at any time. Furthermore, shock-absorbers of the specific type used with physical training appliances for the development and re-training of muscular power, as known heretofore, leave much to be desired. Rubber chest expanders or exercisers are adapted only to withstand traction and cannot offer any resistance to compression. In addition, they are dangerous because if they are suddenly released accidentally they may cause injury to the user. Also, the resistance offered by such exercisers is approximately proportional to their elongation, and this generally prevents the movement of the exerciser to the point of complete contraction of the user's muscle, and this is an important efficiency factor. Excessive elongation of the elastic medium in such exercisers beyond the elasticity threshold, produces slackening of the elastic fibre, which also undergoes progressive aging due to ordinary oxidation. Depending upon their construction, spring exercisers can offer resistance to traction or compression, but they have numerous disadvantages and dangers, including deformation and rapid slackening, dangerous spring-back if handled incorrectly. Furthermore, the risk of tearing cloth, yarn and the skin make it necessary to provide outer sliding tubes for protective purposes. The result is a rudimentary appliance which is non-adjustable, which has restricted use possibilities, and the use of which is dangerous.
Pneumatic appliances based on the principle of air compressibility have recently appeared on the market. These appliances represent some progress in the art but they have inadequacies bound up with the principle of compressibility in the same way as chest expanders and springs.
The invention provides an appliance without the above disadvatages, which is adapted to act as a readily adjustable shock-absorber in various conventional applications and to act as a physical training appliance of high reliability and efficacy, usable both under traction and compression. One of the outstanding properties of the novel appliance is its perfectly inert state of equilibrium in any position and the possibility of locking it rapidly in each of its positions. Consequently, unlike known exercisers, traction and compression forces can be released at any time during use of the appliance without any danger because it simply remains in the state of traction or compression at which it was released. Inter alia, this property opens up new applications to this novel shock-absorber, i.e., as a device for fixing doors, windows or other closure elements or any other means in any desired partially open position. For accomplishing these same purposes very simple, but inconvenient shift devices are known, as are complicated and expensive slide guide devices which are complex to handle. The shock-absorber according to the invention is simple and may be made in very much smaller dimensions so that it advantageously replaces these former devices. A quick turn of a screw enables the appliance to be locked to secure the required partial opening of a door, window or the like.